The present invention relates to a pneumatic tire which can be preferably used as an all season tire and has a traveling performance on an ice and snow road while keeping a traveling performance on a normal road such as wet and dry roads or the like high.
In general, a tire for passenger cars can be classified into a summer tire in which a traveling performance on a normal road such as the wet and dry roads and the like (in some cases called as a summer performance) is taken into consideration, a studless tire in which a traveling performance on an ice and snow road (in some cases called as an ice and snow performance) is particularly obtained, and an all season tire in which both of the traveling performances are taken into consideration.
Here, in the studless tire, in general, in order to provide with a sufficient grip force on the ice and snow road, an adhesion friction force between the tire and the ice surface is increased by employing a block pattern by which a sea area ratio corresponding to a rate of a tread groove occupied in a tread ground plane is increased and forming a multiplicity of sipes in the block so as to increase a road surface scratching and excavating friction force (an edge effect) by the block and an edge of the sipe, or using a soft rubber capable of keeping a flexibility (being excellent in a low temperature characteristic) even at a low temperature for the tread rubber so as to increase an adhesion friction force between the tire and the ice surface.
However, all of these methods tend to widely deteriorate the summer performance mentioned above, for example, cause a reduction of rigidity in the tread portion, make a cornering force insufficient and the like. Accordingly, in the all season tire which is designed by using these methods and has an intermediate nature between the summer tire and the studless tire, the summer performance is largely less than the summer tire and the ice and snow performance is largely less than the studless tire, thereby making it hard to be allowed on the market.
Accordingly, an object of the present invention is to provide a pneumatic tire which can achieve an ice and snow performance while keeping an summer performance corresponding to that of the conventional summer tire and can be preferably used as an all season tire.